This project has as its goal an exploration of the roles that the retinoblastoma family of proteins (pRb, p107, p130), the E2F family of proteins (E2F-1 to E2F-5) and the CBP/p300 proteins play in the regulation of alveolar epithelial cell differentiation. The pRb/E2F proteins have been intensively studied because of their critical role in cell cycle regulation. However, increasing evidence from a number of systems suggests that they also play important roles in cell differentiation. CBP/p300 have recently been described as co-activators of gene transcription and appear to serve as mediators of multisignal transduction pathways. Both pRb and CBP/p300 complex with a number of factors that have the potential to influence lung cell gene expression. These include for pRb, the glucocorticoid response element and the transcription factor C/EBP; for CPB/p300, the cAMP response element, AP-1 and a number of nuclear hormone receptors. The surfactant proteins, T1 alpha and GGT all contain putative binding sites for these elements. We therefore plan to: 1) define the timing and sites of expression of the pRb and E2F gene families in normal and pRb family null mutant mice; 2) examine the role that the E2F-5 gene we have cloned from the lung plays in regulating lung cell proliferation and differentiation; and 3) determine whether CBP/p300 plays an important role in regulating expression of lung epithelial cells. Preliminary studies provide data that supports the rationale for each of this aims. The studies will be carried out using cell lines, in vitro embryonic lung culture systems and transgenic mice. We will focus on how pRb affects expression of the lat alveolar genes, SP-A, SP-D and lysozyme and how CBP/p300 regulates expression of these and other genes being studied in the PPG. The studies we propose continue the goals set forth in the first five years of this Project, which were to explore the relationship between lung epithelial cell proliferation an differentiation, but focus our studies on specific mechanisms.